Holographic Grating Spectrometer for OCT


  • Up to 130 kHz Line Rate via USB 3.0
  • Designed for Easy Integration into OCT Systems
  • 150 nm Bandwidth Around 890 nm Center Wavelength
  • Volume Phase Holographic Transmission Grating Design

HG10

Cables, Power Supply,
and Software Included

OCT Image of Fingertip Cross-Section

Related Items


Please Wait
Thorlabs OCT Group
OCT Applications Team Based in Lübeck, Germany
Contact Button

We are happy to assist with purchasing or information requests. You can easily contact us directly at oct@thorlabs.com or via our online request form; a Thorlabs customer representative will contact you shortly.

HG10 Spectrometer Setup
Click to Enlarge

Diagram Showing the Operation of the HG10 Spectrometer

Features

  • 810 - 965 nm Wavelength Range
  • Incorporates a Volume Phase Holographic Transmission Grating
  • Spot-Size-Limited Design (Diffraction-Limited with Single Mode Fiber Input)
  • High-Speed USB 3.0 Connection Allows up to 130,000 Scans per Second
  • Trigger Input for External Synchronization (TTL)
  • 2048 Pixel Line Scan Sensor
  • Wavelength Calibrated and Shipped with Calibration Report
  • Amplitude Corrected: Relative Correction Based on Pixel Intensity
  • Includes Single Mode Fiber Patch Cable
  • Customizable Center Wavelength and Camera Speed (Please Contact our OCT Support Team)

Thorlabs' HG10 Holographic Grating Spectrometer is a fiber-based, high-speed spectrometer that provides sub-nanometer resolution in the optical range of 810 to 965 nm. Its acquisition speed of up to 130 kHz, external synchronization options via a TTL trigger input, and rigid design make it ideal for stable and rapid spectrum acquisition. The spectrometer is based on the ones used in our Ganymede™ Series of Optical Coherence Tomography (OCT) imaging systems and has been designed to support easy integration into laboratory setups.

This device is a refraction-optics-based spectrometer. The incoming light is collimated to optimize the performance of the volume phase holographic (VPH) grating and guarantee that the light incident on the grating has a flat wavefront. The grating output angle depends on the wavelength, and this effect is used to create a spatial distribution of the spectrum on the camera, as seen in the diagram to the right.

Each spectrometer ships with a USB flash drive, an adapter cable for external trigger signals, a high-speed USB 3.0 cable, and a P3-780A-FC-2 single mode fiber optic patch cable with FC/APC connectors. The unit comes wavelength calibrated and amplitude corrected with the included patch cable prior to shipment. The included USB flash drive contains the software package, calibration report, and calibration certificate. Thorlabs offers a large selection of fiber optic patch cables and bundles that may be purchased separately. Please note that changing the fiber patch cable makes the calibration void; if a replacement or alternate patch cable is required, Thorlabs recommends recalibration using the new cable. Please contact oct@thorlabs.com if you are interested in a spectrometer calibrated with a different patch cable.

The performance data for each spectrometer can be downloaded by clicking on the red Docs icon () next to the Item # and entering your device's serial number under "Download Calibration Data."

Mounting Options
For ease and stability of mounting, the HG10 spectrometer is equipped with a base plate. The base plate has three slots that allow the device to be mounted on standard imperial (1/4”-20 taps) and metric (M6 taps) breadboards and optical tables. If the spectrometer is used as a stand-alone device, four self-adhesive rubber feet are included and can be easily attached in the recesses on the bottom of the base plate. See the Setup tab for more details.

Software
The included software contains built-in tools for simple and complex analysis, including controls for adjusting sensitivity and resolution, a wavelength meter tool for narrowband sources, and a coherence length tool for broadband sources. Apodization functions, which are used to account for the finite path length over which the spectrum is measured, are also available. The ThorSpectra GUI can be used to view the spectra as they are being acquired. The raw data can be exported as is or with user-selected processing applied, including wavelength calibration, interpolation onto an evenly spaced wavelength grid, or relative amplitude correction. For OCT data aquisition, Software Development Kits (SDKs) in several languages are included. Please see the Software tab for additional details on software capabilities.

OCT Imaging with the HG10 Spectrometer
OCT is a noninvasive optical imaging technique that produces real-time, 2D cross-sectional and 3D volumetric images of a sample. This technique provides structural information about the sample based on light backscattered from different layers of material within that sample, producing images with micron-level resolution and millimeters of imaging depth. OCT imaging can be considered as an optical analog to ultrasound imaging that achieves higher resolution at the cost of decreased penetration depth. In addition to high resolution, the non-contact, noninvasive nature of OCT makes it well suited for imaging samples such as biological tissue, small animals, and industrial materials. For more details, see the OCT Tutorial tab.

This spectrometer is well-suited to act as a key component in a Spectral Domain (SD) OCT system to provide high-quality, state-of-the-art images with a high axial resolution of 5.0 µm and 2.5 mm imaging depth. The optics inside the spectrometer have wavelength-specific coatings to ensure high photon efficiency, maximizing OCT sensitivity. The 2048 pixel line sensor is optimized for OCT applications, providing high full well capacity of 140 ke-, high quantum efficiency in the NIR of 54%, and a high scan rate of up to 130 kHz. The OCT cross-sectional image at the top of this page shows a fingertip and was obtained using an HG10-equivalent spectrometer integrated into a Ganymede OCT system.

Custom Spectrometers
Custom spectrometers with detection ranges from 500 to 1000 nm are available. We are able to customize the camera speed from 20 to 250 kHz with a USB or CameraLink interface. Please contact oct@thorlabs.com if you are interested in a spectrometer with a different camera speed, camera interface, resolution, or optical fiber.

Recalibration Service
Thorlabs offers a recalibration service for the HG10 spectrometer (which can be ordered below using Item # CAL-HG). To ensure accurate measurements, we recommend recalibrating every twelve months.

HG10 Spectrometer Drawing
Click to Enlarge

Mechanical Drawing for the HG10 Spectrometer
Specifications
Optical
Detection Range (Typical) 810 - 965 nm 12346 - 10363 cm-1
Spectral Resolution (FWHM)a 0.25 nm 3.16 cm-1
Spectral Accuracy ±0.15 nm ±1.9 cm-1
Pixel Resolutionb 0.08 nm
Wavelength Precision ±0.1 nm
Signal-to-Noise Ratio 40 dB
OCT A-Scan Resolution (FWHM)c 5.0 µm
OCT Imaging Depth 2.5 mm
Stray Lightd <0.1%
Included Patch Cable
Patch Cable Item # P3-780A-FC-2e
Fiber Item # 780HP
Connector FC/APC, 2.0 mm Narrow Key
Numerical Aperture 0.13
Grating
Item # GP3512N
Type Volume Phase Holographic Transmission
Line Density 1200 Lines/mm
Design Wavelength 930 nm
Info Click for Details
Camera
Sensor Type Silicon
Sensor Range 400 - 1100 nm
Interface USB 3.0
Maximum Speed 130 kHz
Minimum Speed 1.5 kHz
Integration Time (Maximum) 654.6 µs
Acquisition Period (Maximum) 655.35 µs
Pixels/Line 2048
Pixel Size 10 µm x 200 µm
Dynamic Range 69 dB
Analog-to-Digital Conversion (ADC) Resolution 130 kHz @ 10 Bit
<120 kHz @ 12 Bit
Readout Noise 55 e-
Full Well Capacity (Typical) 140 ke-
Quantum Efficiency Coefficient 54%
External Trigger
Maximum Frequency 130 kHz
Input Interface BNC
Signal TTL
Input Voltage 0 - 5 V
General
Interface to PC USB 3.0
Dimensions (L x W x H), Without Cable and Fiber 237.0 mm x 174.7 mm x 98.5 mm
(9.33" x 6.88" x 3.88")
Weight (Spectrometer Only) 2.9 kg
Ambient Operating Temperature 10 °C to 35 °C (Non-Condensing)
  • Measured Argon Peaks Within the Detection Range
  • Calculated Value: Bandwidth Over Amount of Pixels
  • If the entire wavelength detection range is used.
  • Quantified using a bandpass filter with an optical density of 4 in the blocking region. The stray light is calculated by comparing the light detected at wavelengths in the filter's blocking regions to the light detected without the filter in place.
  • If the fiber patch cable is switched or replaced, the spectrometer will need to be recalibrated. Thorlabs offers a factory recalibration service, which can be ordered by scrolling to the bottom of the page and selecting Item # CAL-HG.

Mounting Options

For mounting ease and stability, the HG10 spectrometer is equipped with a base plate. The base plate has three slots that allow the device to be mounted on standard imperial (1/4”-20 taps) and metric (M6 taps) breadboards and optical tables. For optimal stability, use multiple slots to secure your device. If the spectrometer is being used as a stand-alone device, four self-adhesive rubber feet are included and can be attached easily in the recesses on the base plate’s bottom side.

Mount on Breadboard with Back Slot
Click to Enlarge

Breadboard Mounting, Step 1: Mount the unit on a breadboard such as the MB3045/M Breadboard above using the slot on the back.

Mount on Breadboard with Side Slots
Click to Enlarge

Breadboard Mounting, Step 2: Secure the unit on the breadboard using one or more of the slots on the side.
Mount Rubber Feet
Click to Enlarge

For Stand-Alone Operation: Attach the self-adhesive rubber feet to the bottom of the spectrometer.

Connecting the Spectrometer

Detailed instructions to connect the spectrometer are provided in each manual (included with each device and accessible by clicking on the red documents icon below).

Connect FC/APC Fiber
Click to Enlarge

Step 1: Connect the included FC/APC fiber to the spectrometer.
Connecting USB, Power Supply, and Optical Fiber
Click to Enlarge

Step 2: Connect the power supply and wait until the Camera LED turns green. Then connect the USB 3.0 cable to the spectrometer and the PC.
Connect Optional Trigger Adapter
Click to Enlarge

Step 3: If needed, connect the trigger adapter cable to use an external trigger or to read the internal camera trigger.

Item # HG10 includes the following:

  • Holographic Grating Spectrometer
  • Power Supply with Region-Specific Power Cord
  • Trigger Cable Adapter, 20 cm
  • BNC Straight Adapter (Item # T3283)
  • Single Mode Optical Fiber with FC/APC Connector, 2 m (Item # P3-780A-FC-2)
  • USB 3.0 Cable Type A/B Micro Cable, 2 m
  • USB Flash Drive
  • Four Rubber Feet
  • Quick Start Guide

Software

Version 1.0.0.4

Software package to operate the HG10 Spectrometer including the ThorSpectra GUI, drivers, and SDKs for third-party development.

Software Download
TC300 Software
Click to Enlarge

Software GUI

Software for the HG10 Spectrometer

  • Operates up to 10 Devices Simultaneously
  • Auto-Detection of Compatible Devices
  • Available Filters: Peak Finder, Smoothing, Averaging, Flip/Revert Picture
  • Algorithms: Gaussian Transformation, Absorbance, Transmittance and Relative Difference Measurement
  • Normalized Y Axis
  • Persistence Option
  • User Wavelength Calibration
  • Optional Amplitude Correction
  • User-Selectable Colors and Shapes
  • Saving and Retrieval of Scans (.spf2 or .csv)
  • Copy to Clipboard Function
  • Printable Windows
  • Tabbed or Floating Windows
  • Polynomial or Gaussian Data Fitting
  • Adjustable Parameters:
    • Integration Time
    • Trigger Modes: Internal, External, Continuous, Single Shot
    • Averaging Method: Gliding or Block Average
    • Smoothing Method: Block Smoothing
    • Picture Flip and Revert
    • Display Mode: nm or Pixel

The HG Software Package, designed for laboratory and manufacturing applications, features the easy-to-use ThorSpectra graphical user interface (GUI). The GUI allows multiple sets of data to be displayed in a single graph for comparison with each other and the background data. With the help of smoothing and averaging algorithms, the user is able to enhance specific features of the spectra. Furthermore, the software is able to control up to ten devices at one time and present the data in a single graph.

The screenshot to the right shows the peaks from a calibration lamp acquired with the HG10 spectrometer. The peaks show the specific wavelengths emitted by the calibration lamp.

Additionally, Thorlabs provides drivers for C, C++, C#, MATLAB, Python, and LabVIEW for more specific demands. The software package supports LabVIEW from version 2017 onwards. Code from earlier versions of LabView will need to be converted to a newer format; if assistance with the conversion is needed, please contact the OCT Support Team.

Data Processing
The software allows stored data to be loaded for comparison. Absorbance, transmittance, or the relative difference can be calculated and displayed.

Software Development Kits (SDKs)
For maximum flexibility, the HG Software offers several possibilities to implement customized solutions using software development kits (SDKs). The libraries can be used in a multitude of programming environments (C, C++, C#, MATLAB, Python, and LabVIEW) and allow the user to directly control the HG system, implement customized data acquisition routines, and execute spectral processing functions. For more information on the architecture of the SDKs, please see the manual.

To facilitate the use and integration of the HG spectrometer all SDKs include code examples covering various scenarios and use cases. The sample programs are commented step by step and are an excellent starting position to develop user defined applications. Besides fundamental functions, regarding initialization, logging and error handling, the examples demonstrate how to:

  • Modify Device Parameters
  • Acquire and Process a User-Selected Number of Raw Spectra
  • Continuously Acquire and Process Data
  • Acquire Data at a Specific Line Rate or Exposure Time
  • Use Callbacks to Acquire Data
  • Write Data Directly to a File or a Sequence of Files
  • Use an External Trigger

Please contact oct@thorlabs.com for details.

Diffraction Gratings Tutorial

Introduction

Diffraction gratings, either transmissive or reflective, can separate different wavelengths of light using a repetitive structure embedded within the grating. The structure affects the amplitude and/or phase of the incident wave, causing interference in the output wave. In the transmissive case, the repetitive structure can be thought of as many tightly spaced, thin slits. Solving for the irradiance as a function wavelength and position of this multi-slit situation, we get a general expression that can be applied to all diffractive gratings when = 0°,

Grating Equation 1

(1)

known as the grating equation. The equation states that a diffraction grating with spacing a will deflect light at discrete angles (theta sub m), dependent upon the value λ, where is the order of principal maxima. The diffracted angle, theta sub m, is the output angle as measured from the surface normal of the diffraction grating. It is easily observed from Eq. 1 that for a given order m, different wavelengths of light will exit the grating at different angles. For white light sources, this corresponds to a continuous, angle-dependent spectrum.

Transmission Grating
Figure 1. Transmission Grating

Transmission Gratings

One popular style of grating is the transmission grating. The sample diffraction grating with surfaces grooves shown in Figure 1 is created by scratching or etching a transparent substrate with a repetitive series of narrow-width grooves separated by distance a. This creates areas where light can scatter.

The incident light impinges on the grating at an angle theta sub i, as measured from the surface normal. The light of order m exiting the grating leaves at an angle of theta sub m, relative to the surface normal. Utilizing some geometric conversions and the general grating expression (Eq. 1) an expression for the transmissive diffraction grating can be found:

Grating Equation 2

(2)

where both and are positive if the incident and diffracted beams are on opposite sides of the grating surface normal, as illustrated in the example in Figure 1. If they are on the same side of the grating normal, must then be considered negative.

 
Reflective Grating
Figure 2. Reflective Grating

Reflective Gratings

Another very common diffractive optic is the reflective grating. A reflective grating is traditionally made by depositing a metallic coating on an optic and ruling parallel grooves in the surface. Reflective gratings can also be made of epoxy and/or plastic imprints from a master copy. In all cases, light is reflected off of the ruled surface at different angles corresponding to different orders and wavelengths. An example of a reflective grating is shown in Figure 2. Using a similar geometric setup as above, the grating equation for reflective gratings can be found:

Grating Equation 3

(3)

where is positive and is negative if the incident and diffracted beams are on opposite sides of the grating surface normal, as illustrated in the example in Figure 2. If the beams are on the same side of the grating normal, then both angles are considered positive.

Both the reflective and transmission gratings suffer from the fact that the zeroth order mode contains no diffraction pattern and appears as a surface reflection or transmission, respectively. Solving Eq. 2 for this condition, theta sub i = theta sub m, we find the only solution to be m=0, independent of wavelength or diffraction grating spacing. At this condition, no wavelength-dependent information can be obtained, and all the light is lost to surface reflection or transmission.

This issue can be resolved by creating a repeating surface pattern, which produces a different surface reflection geometry. Diffraction gratings of this type are commonly referred to as blazed (or ruled) gratings. More information about this can be found in the section below.

Blazed (Ruled) Gratings

Blazed Grating
Figure 4. Blazed Grating, 0th Order Reflection
Blazed Grating
Figure 3. Blazed Grating Geometry

The blazed grating, also known as the echelette grating, is a specific form of reflective or transmission diffraction grating designed to produce the maximum grating efficiency in a specific diffraction order. This means that the majority of the optical power will be in the designed diffraction order while minimizing power lost to other orders (particularly the zeroth). Due to this design, a blazed grating operates at a specific wavelength, known as the blaze wavelength.

The blaze wavelength is one of the three main characteristics of the blazed grating. The other two, shown in Figure 3, are a, the groove or facet spacing, and gamma, the blaze angle. The blaze angle gamma is the angle between the surface structure and the surface parallel. It is also the angle between the surface normal and the facet normal.

The blazed grating features geometries similar to the transmission and reflection gratings discussed thus far; the incident angle () and th order reflection angles () are determined from the surface normal of the grating. However, the significant difference is the specular reflection geometry is dependent on the blaze angle, gamma, and NOT the grating surface normal. This results in the ability to change the diffraction efficiency by only changing the blaze angle of the diffraction grating.

The 0th order reflection from a blazed grating is shown in Figure 4. The incident light at angle theta sub i is reflected at theta sub m for m = 0. From Eq. 3, the only solution is theta sub i = –theta sub m. This is analogous to specular reflection from a flat surface.

Blazed Grating
Figure 6. Blazed Grating, Incident Light Normal to Grating Surface
Blazed Grating
Figure 5. Blazed Grating, Specular Reflection from Facet

The specular reflection from the blazed grating is different from the flat surface due to the surface structure, as shown in Figure 5. The specular reflection, theta sub r, from a blazed grating occurs at the blaze angle geometry. This angle is defined as being negative if it is on the same side of the grating surface normal as theta sub i. Performing some simple geometric conversions, one finds that

Grating Equation 2

(4)

Figure 6 illustrates the specific case where theta sub i= 0°, hence the incident light beam is perpendicular to the grating surface. In this case, the 0th order reflection also lies at 0°. Utilizing Eqs. 3 and 4, we can find the grating equation at twice the blaze angle:

Grating Equation 2

(5)

Littrow Configuration for Reflective Gratings

The Littrow configuration refers to a specific geometry for blazed gratings and plays an important role in monochromators and spectrometers. It is the angle at which the grating efficiency is the highest. In this configuration, the angle of incidence of the incoming and diffracted light are the same, theta sub i = theta sub m, and m > 0 so

Grating Equation 2

(6)

Blazed Grating
Figure 7. Littrow Configuration

The Littrow configuration angle, Theta sub L, is dependent on the most intense order (m = 1), the design wavelength, lambda sub D, and the grating spacing a. It is easily shown that the Littrow configuration angle, Theta sub L, is equal to the blaze angle, gamma, at the design wavelength. The Littrow / blaze angles for all Thorlabs' Blazed Gratings can be found in the grating specs tables.

Grating Equation 2

(7)

It is easily observed that the wavelength dependent angular separation increases as the diffracted order increases for light of normal incidence (for theta sub i= 0°, theta sub m increases as m increases). There are two main drawbacks for using a higher order diffraction pattern over a low order one: (1) a decrease in efficiency at higher orders and (2) a decrease in the free spectral range, Free Spectral Range, defined as:

Grating Equation 2

(8)

 

where lambda is the central wavelength, and m is the order.

The first issue with using higher order diffraction patterns is solved by using an Echelle grating, which is a special type of ruled diffraction grating with an extremely high blaze angle and relatively low groove density. The high blaze angle is well suited for concentrating the energy in the higher order diffraction modes. The second issue is solved by using another optical element: grating, dispersive prism, or other dispersive optic, to sort the wavelengths/orders after the Echelle grating.

Holographic Gratings
Figure 8. Volume Phase Holographic Grating

Volume Phase Holographic Transmission Gratings

Unlike traditional gratings, volume phase holographic (VPH) gratings do not have surface grooves. Instead, VPH gratings consist of a dichromated gelatin (DCG) film between two glass substrates. These VPH gratings are designed to reduce the periodic errors that can occur in blazed gratings. Surface gratings with high groove density also have an issue with polarization dependent loss. These unique transmission gratings deliver high first-order diffraction peak efficiency, low polarization dependence, and uniform performance over broad bandwidths.

The desired grating pattern is comprised of a repetitive series of lines separated by distance a. The fringe planes for transmission gratings are perpendicular to the plane of the plate as seen in Figure 8, allowing any frequency of light to pass through the plate. Diffraction occurs as incoming light crosses through the DCG film. Therefore, the three major factors that determine performance are film thickness, bulk index (the average index of refraction between Bragg planes), and index modulation (the difference of index of refraction between the Bragg planes). The incident light enters the grating at an angle of theta sub i, as measured from the surface normal. The light of order m exiting the grating leaves at an angle of theta sub m, relative to the surface normal. The grating expression mentioned above can be used to calculate diffraction angles for volume phase holographic gratings since dispersion is based on the line density. The quality of the grating is determined by the fringe contrast, with a poor fringe contrast resulting in low efficiency or no grating at all.

The DCG film is taken through multiple quality control steps to ensure it performs up to standard and then cut into the desired size. The film is sealed between two glass covers to prevent degradation of the material. Since the DCG film is contained between two glass substrates, VPH gratings have high durability and long lifetimes, as well as easy maintenance compared to other gratings that can be easily damaged.

Holographic Gratings
Figure 9. Holographic Grating

Holographic Surface Reflective Gratings

While blazed gratings offer extremely high efficiencies at the design wavelength, they suffer from periodic errors, such as ghosting, and relatively high amounts of scattered light, which could negatively affect sensitive measurements. Holographic gratings are designed specially to reduce or eliminate these errors. The drawback of holographic gratings compared to blazed gratings is reduced efficiency.

Holographic gratings are made from master gratings by similar processes to the ruled grating. The master holographic gratings are typically made by exposing photosensitive material to two interfering laser beams. The interference pattern is exposed in a periodic pattern on the surface, which can then be physically or chemically treated to expose a sinusoidal surface pattern. An example of a holographic grating is shown in Figure 9.

Please note that dispersion is based solely on the number of grooves per mm and not the shape of the grooves. Hence, the same grating equation can be used to calculate angles for holographic as well as ruled blazed gratings.

Optical Coherence Tomography Tutorial

Optical Coherence Tomography (OCT) is a noninvasive optical imaging modality that provides real-time, 1D depth, 2D cross-sectional, and 3D volumetric images with micron-level resolution and millimeters of imaging depth. OCT images consist of structural information from a sample based on light backscattered from different layers of material within the sample. It can provide real-time imaging and is capable of being enhanced using birefringence contrast or functional blood flow imaging with optional extensions to the technology.

Thorlabs has designed a broad range of OCT imaging systems that cover several wavelengths, imaging resolutions, and speeds, while having a compact footprint for easy portability. Also, to increase our ability to provide OCT imaging systems that meet each customer’s unique requirements, we have designed a highly modular technology that can be optimized for varying applications.

Application Examples

Art Conservation
Art Conservation
Drug Coatings
Drug Coatings
3D Profiling
3D Profiling
In Vivo
In Vivo
Small Animal
Small Animal
Biology
Biology
Tissue Birefringence
Tissue Birefringence
Mouse Lung
Mouse Lung
Retina Cone Cells
Retina Cone Cells

OCT is the optical analog of ultrasound, with the tradeoff being lower imaging depth for significantly higher resolution (see Figure 1). With up to 15 mm imaging range and better than 5 micrometers in axial resolution, OCT fills a niche between ultrasound and confocal microscopy.

In addition to high resolution and greater imaging depth, the non-contact, noninvasive advantage of OCT makes it well suited for imaging samples such as biological tissue, small animals, and materials. Recent advances in OCT have led to a new class of technologies called Fourier Domain OCT, which has enabled high-speed imaging at rates greater than 700,000 lines per second.1 

Fourier Domain Optical Coherence Tomography (FD-OCT; Figure 2) is based on low-coherence interferometry, which utilizes the coherent properties of a light source to measure optical path length delays in a sample. In OCT, to obtain cross-sectional images with micron-level resolution, and interferometer is set up to measure optical path length differences between light reflected from the sample and reference arms.

There are two types of FD-OCT systems, each characterized by its light source and detection schemes: Spectral Domain OCT (SD-OCT) and Swept Source OCT (SS-OCT). In both types of systems, light is divided into sample and reference arms of an interferometer setup, as illustrated in Figure 3. SS-OCT uses coherent and narrowband light, whereas SD-OCT systems utilize broadband, low-coherence light sources. Back scattered light, attributed to variations in the index of refraction within a sample, is recoupled into the sample arm fiber and then combined with the light that has traveled a fixed optical path length along the reference arm. A resulting interferogram is measured through the detection arm of the interferometer.

The frequency of the interferogram measured by the sensor is related to depth locations of the reflectors in the sample. As a result, a depth reflectivity profile (A-scan) is produced by taking a Fourier transform of the detected interferogram. 2D cross-sectional images (B-scans) are produced by scanning the OCT sample beam across the sample. As the sample arm beam is scanned across the sample, a series of A-scans are collected to create the 2D image.

Similarly, when the OCT beam is scanned in a second direction, a series of 2D images are collected to produce a 3D volume data set. With FD-OCT, 2D images are collected on a time scale of milliseconds, and 3D images can be collected at rates now below 1 second. 

Spectral Domain OCT vs. Swept Source OCT

Spectral Domain and Swept Source OCT systems are based on the same fundamental principle but incorporate different technical approaches for producing the OCT interferogram. SD-OCT systems have no moving parts and therefore have high mechanical stability and low phase noise. Availability of a broad range of line cameras has also enabled development of SD-OCT systems with varying imaging speeds and sensitivities.

SS-OCT systems utilize a frequency swept light source and photodetector to rapidly generate the same type of interferogram. Due to the rapid sweeping of the swept laser source, high peak powers at each discrete wavelength can be used to illuminate the sample to provide greater sensitivity with little risk of optical damage.

FD-OCT Signal Processing

In Fourier Domain OCT, the interferogram is detected as a function of optical frequency. With a fixed optical delay in the reference arm, light reflected from different sample depths produces interference patterns with the different frequency components. A Fourier transform is used to resolve different depth reflections, thereby generating a depth profile of the sample (A-scan).

1V.Jayaraman, J. Jiang, H.Li, P. Heim, G. Cole, B. Potsaid, J. Fujimoto, and A. Cable, "OCT Imaging up to 760 kHz Axial Scan Rate Using Single-Mode 1310 nm MEMs-Tunable VCSELs with 100 nm Tuning Range," CLEO 2011 - Laser Applications to Photonic Applications, paper PDPB2 (2011).


Posted Comments:
No Comments Posted

Holographic Grating Spectrometer

  • 2.0 mm Narrow-Key FC/APC Connector
  • Easily Integrated into a Spectral Domain (SD) OCT System
    • Up to 5.0 µm Axial Resolution with Full IIluminated Sensor
    • Up to 2.5 mm Imaging Depth

The HG10 Holographic Grating Spectrometer is a fiber-based, high-speed spectrometer that provides sub-nanometer resolution. Each spectrometer is wavelength calibrated and amplitude corrected relative to the pixel intensity with its included patch cable, and a calibration report is included on the USB stick shipped with each unit. Note that if a different patch cable is used with the spectrometer, the system (spectrometer and new patch cable) should be recalibrated. This device is easy to integrate into an SD-OCT setup and comes with user-friendly SDKs.

Thorlabs offers a recalibration service for the HG10 spectrometer, which can be ordered below (see Item # CAL-HG).

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
HG10 Support Documentation
HG10NEW!Holographic Grating Spectrometer, 810 - 965 nm
$19,950.00
Today

Recalibration Service for Holographic Grating Spectrometer

Thorlabs offers a recalibration service for our HG10 Holographic Grating Spectrometer. To ensure accurate measurements, we recommend recalibrating the spectrometer every 12 months. When sending the part for recalibration, please include the patch cable that the spectrometer will be used with.

Requesting a Calibration
Thorlabs provides two options for requesting a calibration:

  1. Complete the Returns Material Authorization (RMA) form. When completing the RMA form, please enter your name, contact information, the Part #, and the Serial # of the spectrometer being returned for calibration; in the Reason for Return field, select "I would like an item to be calibrated." If you wish to calibrate your spectrometer with a different patch cable than the one that came with the unit, please list the patch cable Item # in the Further Details field. All other fields are optional. Once the form has been submitted, a member of our RMA team will reach out to provide an RMA Number, return instructions, and to verify billing and payment information.
  2. Enter the Part # and Serial # of the item that requires recalibration below and then Add to Cart. A member of our RMA team will reach out to coordinate the return of the item(s) for calibration. Should you have other items in your cart, note that the calibration request will be split off from your order for RMA processing.

Please Note: To ensure your item being returned for calibration is routed appropriately once it arrives at our facility, please do not ship it prior to being provided an RMA Number and return instructions by a member of our team.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
CAL-HG Support Documentation
CAL-HGNEW!Recalibration Service for Holographic Grating Spectrometer
Part Number:  Serial Number:
$230.00
Lead Time